Hitherto, in the rubber industry, it has been known that when a rubber composition containing a filler such as carbon black is produced, a wet rubber masterbatch is used to improve the workability of the composition, and the dispersibility of the filler. This manner is a manner of: mixing a filler and a dispersing solvent beforehand with each other at a predetermined ratio, dispersing the filler into the dispersing solvent by a mechanical force, mixing the resultant filler-containing slurry solution with a rubber latex solution in a liquid phase and then adding a coagulant such as an acid thereto; and further collecting the resultant coagulate, and then drying the product. When the case of using the wet rubber masterbatch is compared with the case of using a dry rubber masterbatch obtained by mixing a filler with a rubber in a solid phase, the former case gives a rubber composition excellent in filler dispersibility and rubber physical properties such as workability and reinforceability. The use of such a rubber composition as a raw material makes it possible to produce a rubber product, for example, a pneumatic tire decreased in rolling resistance and excellent in fatigue resistant performance.
In the above-mentioned wet rubber masterbatch producing method, a method for removing water originating from the dispersing solvent and the rubber latex solution from the filler-containing rubber coagulate obtained through/after the coagulation step is, for example, a method of subjecting the filler-containing rubber coagulate to solid-liquid separation by, e.g., a filtrating method or centrifugal method, and then using an arbitrarily-selected mixing machine to knead this filler-containing rubber coagulate while the product is heated, thereby dehydrating the product. According to this dehydrating method, as the number of dehydrating, drying and plasticizing steps or such steps is increased or the heating temperature at the time of the kneading is heightened, the wet rubber masterbatch obtained through/after the dehydration can be decreased in water content by percentage. However, when the number of the dehydrating, drying and plasticizing steps or such steps, and calorie and/or mechanical energy applied at the dehydration become large, the resultant wet rubber masterbatch undergoes a cleavage of polymer molecular chains thereof, and other inconveniences, so that the finally obtained rubber composition may be deteriorated in vulcanized rubber properties. Accordingly, in the actual situation, there is a room for making many contrivances in the dehydrating, drying and plasticizing steps or such steps in the wet rubber masterbatch producing method.
Patent Documents 1 and 2 listed below each describe a method of using a twin-screw extruder when a filler-containing rubber coagulate is dehydrated and dried.
Moreover, Patent Document 3 listed below describes a technique of using a screw type dehydrator in which its shaft is not limited in number to dehydrate a mixture of a rubber material and a slurry of an inorganic filler. This screw type dehydrator is a screw type dehydrator including the following: a cylinder having, at an upstream side thereof, a hopper opening through which a matter to be treated is supplied and having, at a downstream side thereof, a discharging opening through which the matter to be treated is discharged; at least one screw shaft rotatably supported by the cylinder; and at least one screw having a crest formed spirally in the external circumferential surface of the screw shaft. This dehydrator is characterized in that: the dehydrator includes a first dehydrating section positioned at the hopper opening side of the cylinder, and a second dehydrating section positioned at the discharging-opening side thereof; the diameter of the screw shaft is made gradually large into the advancing direction of the screw in the first dehydrating section; and pin members are fitted to the second dehydrating section, one of the two ends of each of the pin members being fixed to an inner wall of the cylinder, and the other end being projected in a space between adjacent portions of the crest.